1. Field of the Invention
The present invention relates to a chargeable resin powder which can be used in a toner for developing electrostatic images for use in electrophotography and other charging-based techniques, powder coatings for electrostatic painting, and so on.
2. Description of the Prior Art
In copying machines, etc. based on electrophotography, various dry or wet toners containing a coloring agent, a fixing resin and other substances are used to visualize (develop) the electrostatic latent image formed on the photoreceptor having a light-sensitive layer containing an inorganic or organic photoconductive substance. The chargeability of such toners is one of the most important factors in electrostatic latent image developing systems. Thus, to appropriately control or stabilize the amount of charges of the toner, a charge control agent providing a positive or negative charge is often added to the toner.
Also, in recent years, in the field of electrostatic painting, which is based on the charging phenomenon, the utility of solvent-free powder coatings has drawn attention from the viewpoint of labor saving in regard to painting efficiency, prevention of environmental pollution, ease of paint management, and the like. Electrostatic powder painting methods using powder coatings are classified into the corona charging method, the frictional charging method and the hybrid method. In any method, the paint powder must be given a sufficient amount of charges.
As charge control agents for controlling the charging of (colored) resin powders such as dry toners, there have been used electron acceptors having a good negative charge providing property, such as azo-metal complex dyes, aromatic oxycarboxylic acid-metal complexes and salts thereof, and electron donors having a good positive charge providing property, such as nigrosine dyes, triarylmethane dyes and other basic dyes, quaternary ammonium salt compounds, pyridinium salt compounds, imidazole compounds and polyamine resins.
Concerning electrostatic powder coatings, proposals as to application of charge control agents for electrophotographic toners have been considered to improve painting efficiency. Such proposals include an electrostatic powder coating containing a resin polymer of an azine dye such as nigrosine (dye composition) Unexamined Japanese Patent Publication No. 67563/1985!, a resin powder composition for electrostatic painting containing a charge enhancer such as a metal-containing complex compound (Unexamined Japanese Patent Publication No. 75077/1988), a powder coating composition containing a quaternary ammonium salt as a charge control agent or charge enhancer (Unexamined Japanese Patent Publication No. 212563/1990), a frictionally chargeable powder coating composition containing a nitrogen-containing compound such as a guanamine compound (Unexamined Japanese Patent Publication No. 775/1991), and an electrostatic painting method for a resin shaping product (object to be painted) prepared by kneading a complex of an alkylene oxide polymer and an electrolyte salt soluble therein in polypropylene resin, etc.
However, many toners using conventional charge control agents are faulty; for example, the toner charge distribution is uneven because the charge control agent is incompatible with, or poorly dispersible in, the binder resin for the toner, the resulting charge is not stably retained because the toners environmental stability is insufficient, and the charge stability in multiple repeated use of the toner is insufficient. Therefore, there is a need for development of a black toner or color toner containing a charge control agent or charge enhancer which meets practical requirements for such properties.
In electrostatic powder painting, to improve painting efficiency, it is necessary to provide the powder coating with a sufficiently high amount of charges by corona charging or by frictional charging between the painting machine's inside material (e.g., fluorocarbon polymer tube of a powder gun) and the powder coating. Such powder coating must be electrostatically adhered to iron, glass, plastic or the like and baked at 150.degree. to 250.degree. C. For these reasons, there is a need for a powder coating for electrostatic painting containing a charge control agent excellent in charge providing property and heat resistance.
Developed in view of the above problems in the prior art, the present invention is aimed at providing a chargeable resin powder, a toner for developing electrostatic images and a powder coating for electrostatic painting, all excellent in charge stability, charge providing property and heat resistance.